(AP) — A pediatric surgeon who left The Covenant School in Nashville moments before a shooter opened fire, killing six people, says she is horrified by the gun violence that has plagued the U.S.

Dr. Britney Grayson had just finished regaling children at the small religious grade school about Kenya, where she works on missions, when she drove out of the parking lot looking for a Starbucks. Moments later, the shooter entered the school and opened fire, killing three children and three adults.

After she received a text alerting her to the attack, Grayson took to Facebook to post about what she experienced, writing, “WHY ARE OUR CHILDREN BEING MASSACRED IN THEIR SCHOOLS?!”

If a mass shooting is defined as resulting in the death of four or more people, not including the perpetrator, 175 people have died in 15 such events connected to U.S. schools and colleges since 1999.

The horror of what happened had Grayson rattled hours later.

“It’s a weird feeling, knowing that just if it had happened just moments earlier, one, we might have been victims ourselves, and two, maybe I would have been there to offer immediate care,” she said.

In her post, Grayson wrote that she has operated on a school shooting victim. But, she says, she has never felt as close to the violence as she did this time.

“It’s different when you receive a patient at the hospital. I’m on my turf. I have all my skills and or tools with me and all of the team and everything,” she said. “That is definitely different than what we experienced today.”

Grayson notes that even those who survived Monday’s violence will be forever changed. She says the U.S. is laying the burden of gun violence at the feet of children.

“Physically in the children that died, but also all of the children that were there today,” she said. ”The counseling that’s going to be required and the way that this is going to affect their lives forever.”

Grayson wrote on Facebook that the kids were great and learned about Kenya, some Swahili words and what it means to be a missionary.

Later, when an initial death toll came out, she posted an update: “3 children are confirmed dead. 3 children who learned the word ‘Jambo’ this morning from us in chapel,” she wrote, using the Swahili greeting. “3 children who didn’t have to die. Lord be with us. Lord, be with us.”